This invention relates to an improvement of an anti-squeal shim for use in a disc-brake, more particularly to the provision of an anti-squeal shim excellent in durability as well as squeal preventing effect.
In a disc-brake wherein a pair of friction pad assemblies are urged onto a disc in order to decelerate or stop the rotation of the disc, frequent occurrence of unagreeable noise has been experienced, which is generally denominated squeal.
For preventing this phenomenon not a few attempts have been made, among which placing of a shim, a plate-like piece having an elastic characteristic, between the backing plate of the friction pad assembly and the urging means thereonto, that is a piston or a caliper in some cases, in a sandwiched state are popular ones. The sandwich-like insertion of a shim is considered to be a fairly effective way of preventing the squeal because of its strong vibration restricting function, and widely adopted for the purpose.
It is a piece of soft steel plate thinly coated with rubber on opposite surfaces thereof. Since the backing plate of the pad assembly and the urging means such as piston abut respectively on the rubber coated surface of the shim, rather softly or in a less rigid way, the contact with these members can be made mild or soft, which leads to a decrease or elimination of the squeal caused by the frictional vibration.
Such a rubber coating over the shim surface is, however, liable to be affected by high temperature and high load. Sudden or repeated applying of a disc-brake, which is observed for example when a vehicle runs along a long downward slope, often causes crushing or damage of the rubber coating over the shim by the repetition of the brake operation and in some cases gives rise to deterioration thereof due to frictional heat which is known to produce a temperature as high as 200.degree. C. Such a degeneration of the rubber coating may completely spoil the anti-squeal feature of a shim, bringing about a new problem.